This disclosure relates to an optical cable used for sensing, methods of manufacture thereof and to an article comprising the same. More specifically, this disclosure relates to an optical cable used for sensing temperature and strain, methods of manufacture thereof and to an article comprising the same.
In applications such as offshore oil pipelines, in order to aid in the flow of oil through the pipeline, the pipe is heated and the pipeline temperature controlled. When the pipe with the sensing cable installed is loaded onto a boat, transported and offloaded for deployment, during the steps of the installation process, the pipe can be exposed to both tensile and compressive forces resulting in a positive (+) or negative (−) change in length (strain). The optical fiber cable sensor attached to the pipe must be able to withstand these changes in length without transmitting any detrimental stress onto the optical fiber. Excessive stress on the optical cable due to this mechanical deformation for an extended period of time could result in premature mechanical failure of the optical fiber (which is part of the optical cable). If any of the stress on the optical cable is transferred and permanently imparted to the optical fiber, the accuracy of the temperature measurement in application is adversely affected. It is therefore desirable in cable design to reduce the strain that the optical fibers experience during installation to avoid any detrimental effect to the reliability of the optical cable.
In addition, in offshore applications the pipeline may see temperatures fluctuations as low as −30° C. and up to +120° C. These temperature changes will cause the fibers to expand (+) and contract (−). It is desirable to permit the fibers to expand or contract while isolating the sensing optical fibers from mechanical or environmental strain or compression in order to ensure both accuracy in temperature measurements and to assure long-term survival following manufacture and installation. It is therefore also desirable for cable design to accommodate stresses induced by the deformation caused by temperature change.